As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine, such as a milling or boring machine, to securely hold a cutting tool upon the machine during the cutting of a workpiece. In most prior art tool holders, a central aperture is formed therein for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine. Subsequent to the insertion of the shank portion of the cutting tool into the central aperture, the tool holder is drawn or pulled tightly into the spindle so as to rigidly maintain the cutting tool within the tool holder and the machine.
However, prior art tool holders suffered from deficiencies resulting from the manner in which the shank portion of the cutting tool is secured within the central aperture of the tool holder, thereby often resulting in non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is extremely undesirable, particularly in modern, high tolerance machining applications such as those performed on a vertical milling machine wherein minor variations in the concentricity of the cutting tool within the tool holder oftentimes results in extreme flaws in the cutting operation.
Recently, heat shrink tool holders and have gained popularity in high tolerance machining applications for their ability to mount a cutting tool concentrically within the tool holder. In such tool holders, the central aperture is sized slightly smaller than the diameter of the shank of the cutting tool. The cutting tool is only insertable into the central aperture when the tool holder has been heated to the temperature necessary to thermally expand the central aperture to a size which can accept the cutting tool shank. Subsequent to the insertion of the shank thereinto, the tool holder is allowed to cool to ambient temperature, thereby decreasing the size or diameter of the central aperture and rigidly maintaining the cutting tool shank within the tool holder.
Additionally, heat shrink extensions have been used to interface cutting tools to tool holders. Such extensions are typically formed with a bore extending axially within one end, with the opposite end being insertable into the tool holder of the milling or boring machine. Similar to the central aperture of the heat shrink tool holder, the bore of the extension is sized slightly smaller than the shank of the cutting tool such that the shank is insertable therein only when the extension is heated to a temperature sufficient to thermally expand the bore to a size which can accept the tool shank. Subsequent to the insertion of the shank thereinto, the cooling of the extension and resultant thermal contraction of the bore creates a metal to metal press fit between the extension and the shank of the cutting tool, thereby rigidly securing the cutting tool to the extension.
However, prior art heat shrink extensions suffer from a particular deficiency which detracts from their overall utility. More particularly, in such prior art extensions, the cutting tool shank is typically not fully drawn into the bore of the extension as the same is cooled to ambient temperature, thus resulting in the creation of a "gap" between the cutting head of the cutting tool and the extension. In view of this gap, the cutting head of the cutting tool is not in metal to metal contact with the extension, nor is the shank of the cutting tool completely supported by the extension in that a portion of the shank between the extension and the cutting head of the cutting tool is exposed. As will be recognized, the unsupported portion of the shank is more susceptible to being sheared off during horizontal milling operations. Additionally, the gap between the cutting head of the cutting tool and the extension is not desirable since in vertical milling and boring operations, metal to metal contact between the cutting head and the extension is needed to provide the strongest union between these two components and to insure a consistent depth of penetration of the cutting head into a work piece. The problems associated with the formation of the above-described gap not only occur in relation to the use of heat shrink extensions, but also when inserting a cutting tool into a prior art heat shrink tool holder. Thus, there exists a need in the art for heat shrink extensions or tool holders that prevent the formation of a gap between the cutting tool and the extension or tool holder upon the same being cooled to ambient temperature.
The present invention addresses the deficiencies in prior art heat shrink extensions by providing a heat shrink extension which, when cooled to ambient temperature, is adapted to eliminate any gap or void between the extension and the cutting head of the cutting tool which is inserted thereinto. Importantly, the interface provided on the extension to eliminate the gap may also be incorporated into the cutting tool itself, or to a heat shrink tool holder. Whether included on the extension, the tool holder, or the cutting tool, the purpose of the interface is to eliminate any gap between the extension or tool holder and the cutting tool attributable to the heat shrink engagement technique, thus providing the strongest union between the connected components.